Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power).
A wireless communications network may include a number of network devices, e.g., an access point (AP), that can support communication for a number of wireless devices. A wireless device may communicate with a network device bi-directionally. For example, in a wireless local area network (WLAN), a station (STA) may communicate with an associated AP via downlink and uplink. The downlink (or forward link) refers to the communication link from the AP to the station, and the uplink (or reverse link) refers to the communication link from the station to the AP.
In some cases, wireless transmissions may be prepended by a guard interval separating data symbols. Use of a guard interval may result in a lower data rate because the associated time and frequency resources may not be used for transmitting new data. However, the guard interval may mitigate inter-symbol interference (ISI). For example, a guard interval may reduce ISI caused by channel spread (i.e., some frequency ranges of a signal may reach a receiver after a delay caused by multipath signal propagation). A wireless device (either the transmitter or the receiver) may also use the guard interval period to perform finite impulse response (FIR) filtering on a signal. In some cases, the guard interval may be longer than the sum of the channel spread, FIR filter period and other useful delay periods. This may result in excess unused transmission time overhead.